[Newsquest = Science Reporter Kim Hyeong-geun]Bats that live in dark caves have almost deteriorated eyesight, but their hearing is very good. They rely on their hearing to recognize each other and find food.
The squeak coming out of its mouth is reflected elsewhere, and when it hears the sound bounce back, it can fly without bumping into obstacles.
So, since bats live and judge everything by these echoes, people have assumed that there will be no hearing loss throughout their lives. But time has no business.
Many mammals suffer hearing loss in old age
Many mammals, not just humans, suffer hearing loss in old age. Bats, on the other hand, were thought to be immune from this hearing loss because of the importance of hearing for echolocation.
But a team led by Tel Aviv University (TAU) in Israel recently discovered that bats, like other mammals, including humans, lose their hearing as they age.
Bats, which are active in the dark, intermittently emit ultrasonic waves of 30,000 to 60,000 Hz from their vocal cords, and detect the distance, direction, size, etc. of the object by capturing the reflected ultrasonic wave with their ears.
In whales and dolphins, echolocation is achieved by ultrasound in the same way, and it is also used for communication between individuals of the same species. It is used for spatial cognition and behavior in many other animals.
Because bats, like humans and other mammals, nest in very noisy groups that can quickly damage their hearing, it is possible that they have developed an innate ability to limit age-related hearing loss.
Professor Yossi Yovel, a neuroecologist at TAU who led the study, explained: “High-frequency hearing provides a survival advantage for many animals. It is essential for the survival of echolocating bats, which rely on it for orientation.” .
“However, to date, no studies have systematically investigated the effects of aging on bat hearing,” Yobel said.
The team assessed the age of 47 wild Egyptian fruit bats (Rousettus aegyptiacus) by measuring the accumulation of age-related chemical markers in their DNA.
They then tested their hearing by monitoring the responses of the bats’ brains to sounds of various pitches and volumes.
Like humans, they feel impaired by high-frequency sounds.
The analysis found age-related hearing loss to be more pronounced at higher sound frequencies, similar to aging humans. Moreover, the rate of hearing loss (regarding 1 dB per year) was also similar to that observed in humans.
The research team also conducted additional experiments to find that bats They found that the speed of auditory nerve processing decreased, and the structure and function of the cochlea declined.
It’s a condition known as “neuronal presbycusis,” which impairs language comprehension in humans and can make echolocation more difficult in older bats.
The research team pointed to persistent and cumulative exposure to high noise levels in the environment as one possible cause of hearing loss in bats.
The research team installed a microphone in the cave and found that it was continuously exposed to noise of over 100 dB. However, the loudest noises appear to come from bats at lower frequencies unrelated to age-related hearing loss.
Prof Yobel noted that because Egyptian fruit bats rely as heavily on vision as possible, further research is needed to explore hearing loss in bat species with poor eyesight, where echolocation is the primary mechanism for orientation.
“A better understanding of hearing loss in bats might provide new insights into age-related hearing loss in humans,” he explained.
The study was published in a recent issue of the journal Life Science Alliance.